In motor vehicle bodies such as the van type having a lift type tailgate (also called liftgate) that is swung about a horizontal hinge axis at its upper edge to open and close a large rear access opening, it is desirable to have a power actuator for operating the tailgate to relieve a person of the required tailgate operating effort and also as a matter of convenience. Because the tailgate must be lifted upward to open as compared to a tailgate that is hinged about a vertical axis and thus has its weight supported by its hinges, the opening effort required for the former is relatively large because of its unsupported weight and could present a major effort for some people and particularly those with a physical disability. The weight of the tailgate can be offset with counterbalancing devices but a powered tailgate is preferred for convenience as well as serving the disabled. Various forms of powered actuators such as a motor powered linkage system, cable system and crank arm system could be adapted to operate such a tailgate. However, during such powered movement, the tailgate may unexpectedly encounter an obstacle in its path during both opening and closing movement and it is desirable to cease its powered movement in that event to prevent damage to the obstacle and/or the tailgate and its power actuator.
A powered tailgate system that has been proposed and includes a feature for stopping the tailgate movement in such an event is disclosed in co-pending U.S. patent application Ser. No. 08/292,662 filed Aug. 18, 1994 and assigned to the assignee of this invention. In this system, a powered actuator with a reversible DC motor and a worm gear driven crankarm, efficiently operates the tailgate through a roller and guide with gas spring assist. The motor current is monitored by a control circuit that interrupts the power to the actuator motor to stop the tailgate when the current exceeds a certain level as occurs when the tailgate encounters an obstacle. While this system has proven adequate, it has been found that certain further precautionary features with respect to the tailgate operation are desirable and that they can be accomplished in a very cost effective manner with this type of tailgate actuating mechanism.